Mesoporous silica monolith based colorimetric probes for Co2+ ions

[Display omitted] •Facile fabrication of mesoporous silica monolith architect immobilized with TDQ probe.•Solid-state sensor offers excellent selectivity and sensitivity for the optical sensing of Co2+ ions.•Sensor offers real-time and in-situ sensing of ultra-trace Co2+ in real water samples.•Monolithic sensor is eco-benign, reusable, durable, super-responsive, and cost-effective. This article illustrates an eco-friendly approach towards selective and sensitive analysis of Co2+ using solid-state optical sensors by exploiting the surface and structural properties of a continuous 2D hexagonal honey-comb structured mesoporous silica monolith, as probe anchoring templates. An in-house synthesized hydrophobic Co2+ sensing probe i.e., 7-(thiazol-2-yldiazenyl) quinolin-8-ol (TDQ) is immobilized onto the monolith template, through physisorption. The TDQ probe exhibits a strong ligand to metal charge-transfer complex with Co2+, with a binding constant value of 2.5 × 105 M−1, thus providing a significant visual colour change from light orange to bright red. The sensor is efficient for the direct analysis of Co2+ from environmental samples, without requiring laborious preconcentration protocol.